Using the `dtime` value entirely, this will stop the clock
if the game is paused in singleplayer. Since most of the
clocks were fixed a long time ago, this should again be
safe to use.
* squashed: CSM: Implement register_globalstep
* Re-use fatal error mechanism from server to disconnect client on CSM error
* Little client functions cleanups
* squashed: CSM: add core.after function
* core.after is shared code between client & server
* ModApiUtil get_us_time feature enabled for client
